The reason why you use aluminum foil when baking is to allow for even heat distribution to the food and prevent the food from drying out by trapping in moisture.
The aluminum foil is an excellent heat conduction and it also helps with cleanup by preventing food from sticking to baking pans and helps the food cook more evenly and retain moisture while also protecting the baking pan.
The reason some ovens say do not use foil is because you're not supposed to line the bottom of the oven with foil as it can disrupt the heat flow and potentially damage the heating elements.
The aluminum foil can cause the heating elements to overheat as a result of the reflective surface of the foil.
The foil can also melt onto the surface of the oven and cause permanent damage.
You can use aluminum or tin foil in the oven for cooking foods as long as you don't line the bottom of the oven with the foil.
The oven saying do not use foil is referring to not using the foil for the oven itself.
If you want to use foil when cooking food on the pans or baked dishes you can do so.
If you do need to line the bottom of the oven for easy cleanup and can't use foil then you can use parchment paper instead as it can also withstand the high heat temperatures of the oven without causing any issues.
Lining your oven with foil will also increase the intensity of heat that will result in surface damage and even go as far as preventing even cooking.